1. Field of the Invention
The present invention relates generally to a keypad and a keypad assembly that can provide increased flexibility.
2. Description of the Related Art
As various types of portable devices are released, user portability of such devices is an increased concern. Also, the development of a digital convergence technology for integrating multiple portable devices into one has resulted in a tendency to integrate multiple functions into a portable wireless terminal.
For example, many recently-released products have a structure in which an MPEG-Layer Audio 3 (MP3) player, a digital camera, and a game device, are integrated into one portable wireless terminal. Integration of each device's own input keys into a keypad assembly of the portable wireless terminal has became a very difficult problem.
Accordingly, for convenience, the mounting of a general QWERTY type keypad arrangement including various input symbols, such as consonants/vowels, alphabetic letters, numbers, special characters, has a tendency to increase. However, since the size is limited due to the slimness and miniaturization of the portable wireless terminal, the number of key tops of the keypad assembly to be mounted must be restricted.
Presently, such a problem is solved by marking several symbols on each key top or by software, but this causes great inconvenience to a user due to low visibility, for example.
To solve this problem, a technology on such a keypad assembly using electronic paper was disclosed in Korean Patent Laid-open Publication No. 2008-006920 entitled “A Keypad And A Keypad Assembly” (dated Jul. 14, 2006) filed by the present assignee.
Also, this technology was disclosed in U.S. Pat. No. 7,053,799 entitled “Keypad with Illumination Structure”, to Yu et al.
FIG. 1 illustrates a keypad provided with electronic paper according to the prior art.
Electronic paper 14 is disposed such that the upper surface of the electronic paper faces the lower surface of a light guide layer 13, is illuminated by the light emitted from the light guide layer 13, and displays multiple symbols. Herein, the symbols include consonants/vowels, alphabetic letters, numbers, special characters, icons (e.g. a clock, or a telephone), for example. Each symbol displayed on the electronic paper 14 is shown through a corresponding key top 11. The electronic paper 14 includes a lower electrode layer 14a, an ink layer 14b, and an upper electrode layer 14c having transparence in visible light, which are sequentially layered.
The electronic paper 14 has multiple display areas one-to-one corresponding to the key tops 11, and each of the display areas displays at least one symbol (e.g. ‘L’ and ‘C’). For the display of such a symbol, the lower electrode layer 14a has multiple electrode patterns one-to-one corresponding to the display areas, and each of the electrode patterns includes multiple segments. Also, each of the electrode patterns has the same shape as the corresponding symbol. Voltage is applied to each of the electrode patterns with a segment unit.
For example, a ‘C’-shaped electrode pattern has three segments, and displays ‘C’ or ‘L’ through the segment-based voltage application.
Otherwise, each of the electrode patterns may include a single segment. When voltage is applied to the lower electrode layer 14a, the ink layer 14b displays a colored or black/white symbol through the movement of particles according to an applied electric field (that is, the electrophoresis). For example, with electrophoretic electronic paper 14 (E ink corporation), microcapsules filled with transparent liquids separately containing white and black particles are disposed between the upper electrode layer and the lower electrode layer, and the application of an electric field to each of the microcapsules displays a black/white pattern. Since the white particles are positively charged, and the black particles are negatively charged, they move in two opposite directions according to the applied electric field. The electronic paper 14 may display a black/white symbol or a colored symbol, which may be implemented by layering a color filter on the ink layer 14b, using colored particles, instead of black/white particles, as particles constituting the ink layer 14b, or using a colored Light Emitting Diode (LED) or Red, Green, Blue (RGB) light emitting diodes as the light emitting device (not shown). The upper electrode layer 14c functions as a common electrode.
However, the above described keypad assembly using the electronic paper has the following problems.
First, the click feeling is of poor quality because the keypad assembly has a structure where a part of the electronic paper 14 directly presses a corresponding switch by a user's pressing on the key top 11.
Second, the repetitive clicks of the key top 11 may cause the deformation or damage of the electronic paper 14.
Since the light emitting device is disposed between a housing and a transparent keypad, it is difficult to inhibit a light leakage phenomenon.
Third, when a large number of light emitting devices are provided to uniformly and brightly illuminate the electronic paper 14, both the power consumption and the production costs increase.
Fourth, on the lower electrode layer 14a of the electronic paper 14, a projection having a predetermined height from the lower electrode layer 14a is formed due to signal lines according to the electrode patterns of the electronic paper 14.
Accordingly, as the key top 11 is pressed, the electronic paper 14 is bent, and thus force is concentrated on the signal lines at the lower surface of the lower electrode layer 14a. When the lower electrode layer 14a is pressed, a deformation or damage of the electronic paper 14 is incurred.
Therefore, a keypad and a keypad assembly, which can provide the flexibility for a flexible reflective display device, such as electronic paper, are required. Also, in order to minimize the flexible reflective display device's deformation or damage caused by repetitive button clicks, a keypad and a keypad assembly, which have improved impact resistance, are required.